Indeed, Caccini boasts of having invented the genre himself, although there are some examples prior to his publications entitled 'Nuove Musiche' in 1602 and 1614.
The new monodic style involved a virtuoso high voice with written-out ornaments, accompanied by simple chordal bass.
This new separation in function was of course integral to the subsequent development of Baroque music as a whole. Although one cannot give Caccini the full credit he thought he deserved, his importance can hardly be over-stated.
He is featured prominently in any historical anthology of song forms which includes the 17th century.
Todd McComb